How similar, to learn, is Khmer and Thai?

Not the same at all.

Completely different.

The only 2 languages in the region that are similar are Thai and Lao.
Isaan Thai (north eastern Thailand)is very similar to Lao as the Isaan region was once part of Laos. 

I have little problem in NE Thailand when speaking Lao but it is much harder in Bangkok. My Lao wife has same problem when we are in Bangkok or Phuket.

Ahhh...thanks.

But I'm still wondering.  Does Khmer have a 'cat meow' quality that Thai does?  I assume it's a tonal language, right?

Does it have similar phonetics at all?

Regards,
Art

p.s. It's interesting...you mentioned Lao.  We had a Thai take-out restaurant in NW/W Houston that was pretty popular.  I used to love to eat there because I really like Thai food and I was very surprised to learn one day that the owners were actually Laotian.

Is the food in Cambodia similar to Thai...they eat curry, don't they?